1. Field of the Invention
This invention relates to a thin magnetic element comprising a coil pattern formed on a substrate and a thin magnetic film formed on the coil pattern; and a transformer equipped with the element.
2. Description of the Related Art
Reflecting the size reduction and performance improvement of a magnetic element, a soft magnetic material is required to have a high magnetic permeability at a frequency not lower than several hundreds MHz, particularly, to have a high saturation magnetic flux density of 5 kG or higher and at the same, high specific resistance and low coercive force. In a transducer, among various applications, a soft magnetic material having a high specific resistance is especially requested.
As magnetic materials having a high saturation magnetic flux density, Fe and a number of and alloys composed mainly of Fe are known. When manufactured using such an alloy by the film forming technique such as sputtering method, the thin magnetic film so obtained has a high coercive force and small specific resistance in spite of a high saturation magnetic flux density and it is difficult to obtain good soft magnetic properties in a high frequency region. In addition, ferrite frequently employed as a bulk material does not provide excellent soft magnetic properties when formed into a thin film.
As one of the causes for the reduction of a magnetic permeability at high frequency is a loss caused by the generation of an eddy current. For the prevention of such an eddy current loss which is one of the causes for the reduction the magnetic permeability at high frequency, there is accordingly a demand for a reduction in the film thickness and an increase in the resistance of a thin film.
It is however very difficult to heighten the specific resistance while maintaining the magnetic properties. A soft thin magnetic film formed of a crystal alloy, for example, Sendust or an amorphous alloy has a specific resistance as small as several tens .mu..OMEGA..multidot.cm. There is accordingly a demand for soft magnetic alloys having an increased specific resistance with a saturation magnetic flux density being maintained at 5 kG (0.5 T) or greater.
When a soft magnetic alloy is formed into a thin film, it becomes more difficult to obtain good soft magnetic properties owing to an influence of the generation of magneto striction, or the like.
Particularly in the case where a thin magnetic element is formed by disposing a thin film of a soft magnetic alloy close to a coil, it is still more difficult to obtain a high inductance and figure of merit while maintaining good soft magnetic properties which the soft magnetic alloy originally has possessed and also to control a temperature rise during use. In the conventional thin magnetic element of such a type, a loss increase occurs in the thin film formed of a soft magnetic alloy prior to the lowering in the figure of merit Q of a coil itself constituting a magnetic core, resulting in the tendency to limit the high-frequency properties which a transducer or reactor should have as a thin magnetic film. In other words, the application, as a thin magnetic film, of a Co-group amorphous thin film, a Ni-Fe alloy thin film or the like which has excellent soft magnetic properties can be considered but such a thin film does not have a high specific resistance and is apt to increase a loss at high frequency, whereby the high-frequency properties of the entire magnetic element tend to be limited.